New research reveals surprising birthing behavior and expanded calving zones for humpback whales
For years, marine biologists believed that humpback whales only gave birth in warm tropical waters. But a groundbreaking study has uncovered that many humpback whale calves are actually born thousands of kilometers further south, even while the mothers are still migrating.
According to researchers from the University of New South Wales, humpback whales are now giving birth as far south as Tasmania and New Zealand—regions previously not recognized as calving grounds.
“Hundreds of calves were born well outside the known tropical breeding areas,” says Dr. Tracey Rogers, senior author of the study published in Frontiers in Marine Science.
Whales Giving Birth on the Move
Lead researcher Jane McPhee-Frew, a Ph.D. candidate and marine guide, recalls a key moment in July 2023. While leading a whale-watching tour near Newcastle Harbor, one of Australia’s busiest ports, she spotted a tiny newborn calf swimming with its mother.
“It was clearly just born. But none of my fellow guides were surprised—suggesting this behavior might be more common than we thought,” said McPhee-Frew.
A Wider Calving Range: What the Data Says
Following this observation, the team analyzed data from multiple sources including:
- Citizen science platforms
- Government whale surveys
- Whale stranding reports dating back to 1991
The results were eye-opening. Researchers identified 209 verified reports of newborn humpback calves, including:
- 11 confirmed births
- 41 strandings
- 168 live calf sightings
Most notably, some whales gave birth while continuing to migrate north, even from southern locations like:
- Port Arthur, Tasmania (the most southern birth on record)
- Kaikoura, New Zealand
Why Would Whales Give Birth in Cold Waters?
Traditionally, humpback whale migration is thought to be driven by the need to deliver calves in warm, calm tropical waters—ideal for newborns that cannot regulate their body temperature or swim strongly.
But the new study raises important questions:
- Why risk giving birth in cooler, more dangerous waters?
- Could other environmental or biological factors be influencing migration patterns?
While the answers remain unclear, the team suggests that migration might serve more than just calving needs—possibly related to food availability or predator avoidance.
A Conservation Wake-Up Call
With increasing numbers of humpback whales recovering from past hunting, more unusual sightings are being documented. McPhee-Frew points out that the population boom (now estimated at 30,000 to 50,000 in Eastern Australia) may have helped reveal these long-hidden behaviors.
“We believe these births during migration always happened, but the population was too small to detect the pattern until now.”
The findings also carry critical conservation implications:
- Some calves were found injured, likely due to environmental hazards or vessel traffic.
- New calving zones demand expanded marine protected areas.
- Increased public awareness and marine policies are needed to safeguard these vulnerable young whales.
Humpback Whales and the Role of Citizen Science
Much of this new understanding is thanks to whale watchers, marine guides, and public contributions on social media. However, the researchers caution against over-interpreting the data:
“Just because we see more calves in certain areas doesn’t mean more are born there—it could just be more eyes and cameras in those regions,” says Dr. Vanessa Pirotta of Macquarie University.
Final Thoughts: There’s Still So Much to Learn
This study is a reminder that our oceans hold many secrets, and that even well-known species like the humpback whale can surprise us. With continued observation, research, and public involvement, we can improve protection efforts and deepen our understanding of marine mammal behavior.
📘 Reference:
Humpback whales (Megaptera novaeangliae) continue migration after giving birth in temperate waters in Australia and New Zealand, Frontiers in Marine Science, 2025. DOI: 10.3389/fmars.2025.1545526